Measurement of 15N–1H bond lengths by rotational-echo double-resonance NMR spectroscopy

A method based on rotational-echo double-resonance (REDOR) NMR is proposed to measure 1H–15N bond lengths under magic-angle-spinning. Protons are selectively polarized and evolve under the frequency-switched Lee–Goldburg (FSLG) homonuclear decoupling, while two 15N π pulses are applied to restore 1H–15N dipolar interactions. Such a method relies on the 1H–15N dipolar couplings and requires no knowledge of their chemical shift tensors allowing one to precisely extract their couplings. This method could be applicable for measuring relatively long distances between amide protons and other nucleus such as 13C if applying the π pulses to 13C.